1. Field of the Invention
The present invention relates to a Plasma Display Panel (PDP), and more particularly, the present invention relates to a PDP that can improve a bright room contrast by increasing a black region ratio using a subtractive color effect while maintaining a high luminance and light emission efficiency.
2. Description of the Related Art
A Plasma Display Panel (PDP) is a display device that can display an image using red, green, and blue visible light created by exciting phosphors using Vacuum UltraViolet (VUV) rays emitted from a plasma created by a gas discharge.
For example, in an Alternating Current (AC) PDP, address electrodes are formed on a rear substrate. The address electrodes are covered by a dielectric layer. Barrier ribs are arranged in a stripe pattern on the dielectric layer between the address electrodes. Red, green, and blue phosphor layers are formed on the barrier ribs and the dielectric layer. Display electrodes having sustain and scan electrodes crossing the address electrodes are formed on a front substrate facing the rear substrate. The display electrodes are covered by a dielectric layer and an MgO protective layer. Discharge cells are formed at regions where the address electrodes formed on the rear substrate cross the display electrodes formed on the front substrate. More than several millions of unit discharge cells are arranged in a matrix pattern in the PDP.
A memory property is used for driving the discharge cells of the PDP. In more detail, in order to generate the discharge between the sustain and scan electrodes constituting a pair of display electrodes, a potential difference higher than a specific voltage is required. This boundary voltage is called a firing voltage (Vf). When scan and address voltages are respectively supplied to the scan and address electrodes, the discharge is initiated to form a plasma in the discharge cell. Electrons and ions of the plasma travel to electrodes having polarities opposite to those of the electrons and ions.
A dielectric layer is deposited on each electrode of the PDP so that most of space charges are accumulated on the dielectric layer having an opposite polarity. As a result, since the net space potential between the scan and address electrodes is lower than an initially supplied address voltage (Va), the address discharge is weakened and disappears. A relatively small amount of electrons is accumulated on the sustain electrodes and a relatively large amount of electrons is accumulated on the scan electrodes. The charges accumulated on the dielectric layer covering the sustain and scan electrodes are called wall charges (Qw). A space voltage generated between the sustain and scan electrodes by the wall charges is called a wall voltage (Vw).
When a discharge sustain voltage (Vs) is supplied to the sustain and scan electrodes and a sum (Vs+Vw) of the discharge sustain voltage (Vs) and the wall voltage (Vw) is higher than the firing voltage (Vf), a sustain discharge occurs in the discharge cells, thereby generating vacuum ultraviolet rays. The vacuum ultraviolet rays excite the corresponding phosphor layer to emit visible light through the transparent front panel.
However, when there is no address discharge between the scan and address electrodes (i.e., when no address voltage (Va) is supplied), the wall charges are not accumulated between the sustain and scan electrodes. Consequently, no wall voltage exists between the sustain and scan electrodes. At this point, only the discharge sustain voltage (Vs) supplied to the sustain and scan electrodes is formed in the discharge cells. Since the discharge sustain voltage is lower than the firing voltage (Vf), the gas space defined between the sustain and scan electrodes cannot be discharged.
For the PDP driven as described above, there has been a variety of efforts for enhancing the bright room contrast by increasing a black region ratio, i.e., a ratio of an area taken by black with respect to an entire area.
For example, a method using a subtractive color effect has been developed. However, in order to use this subtractive color effect method, a colored layer is provided in front of the phosphor layer, i.e., the discharge cell, emitting the visible light.
The colored layer provided in front of the discharge cell increases the black region ratio in the PDP or a dark area, and thus the bright room contrast is enhanced. However, the colored layer intercepts the visible light to deteriorate the luminance and light emission efficiency of the PDP.